Auto Top-off System

One question I'm asked quite often is how does an
"auto top-top" work. This is a method that can add more freshwater to
your aquarium automatically. The benefit of this is that your tank will
remain more stable as salinity remains at the same level because new
water is replacing what has evaporated.

Others set up a system so that if they go on a short vacation, the tank
will be taken care of.

I'm going to show you what I've been using for three
years or longer with no problems. Needless to say, there are many other
methods that can be safer or more complex depending on your needs. This
system can be built for about $20 to $30 depending on what you own already.
Please read through this completely, perhaps even twice.

I use an electrical float switch that can be purchased
online for $6 plus shipping. You might order two, since they are
cheap and if it fails or you ruin it, you'll have another.

Parts List:

float switch
6' extension cord

2 wire nuts
some flexible tubing

small powerhead
water holding container

Take the extension cord, and at the middle, carefully
separate the two wires. You can do this by cutting between the two with
a razor blade / utility knife. Cut about 4". Now cut one wire in
half. The other wire is left intact. It should not matter which wire
you cut. (I shouldn't have to say this, but do not cut the cord if it
is plugged in! If you get shocked or electrocuted, don't blame me.)

Strip off a little bit of the plastic shielding on
each end from the wire you cut in half.

Thread your float switch through whatever bracket you've designed, and
then use one wire nut to connect the red wire from the float switch
to one of the wires that you bared. Now connect the other red wire to
the other wire. Make sure the wire nuts are tight and you can't tug
any wires loose. Now take a baggie and put it over the wiring you spliced
and wrap it with electrical tape or secure it with a zip tie. This makes
the connection water resistant, as spashes and accidents occur. DONE!

Install the float switch in your sump (or your display
tank if you don't use a sump) in a spot where it will not be knocked
loose. This is extremely important. It should be secured in a permanent
way (example), and you should take care to prevent anything from touching it
such as a wandering snail. It can snack on some nearby algae and then
park there while your sump overflows. If you put the float where you
have snails, you might have to create a snail guard. The float's location
will be the water level in your sump or tank, so you'll want to figure
that out before you secure the bracket.

Insert some flexible tubing into the outlet of the
small powerhead. You'll have to find tubing and a pump that match, but
it shouldn't be hard to find something that will work. Remember, the
pump can be very small because it doesn't need to be strong.

Plug the powerhead into the end of the extension cord,
and put it in your container of water.

Position the other end of tubing in your sump or in
your tank, but affix it so it can't accidentally move. It should pour
water into your system, not the nearby floor. The tubing must remain
above water level, so that it will pour into your system. If it becomes
submerged, it will create a siphon which will either drain all your
freshwtaer into your system, or drain the water from your tank inot
the container. Just keep it 1" off the water and you'll be fine.

Plug in the extension cord of your float switch assembly
into a power source. Test the float by pressing it down. The powerhead
should turn on, and when you lift the float, it will shut off.

How does it work?When the float switch drops down, it completes the circuit
and the outlet on the end of the power cord is now live and will run
anything you've plugged into it. As a kid, we always tested if an
outlet worked with a hair dryer. So that is what I did with my first
float switch, and immediately burned it up. 1500w of power is too much
for these switches, so if you feel the need to test it, use a 100w lamp
or something like a clock radio. But I digress... When the float
switch rises, the power cord goes dead.

Here are some visuals

First of all, here is the entire setup ready to install. The acrylic bracket was made to span my glass
sump, because I couldn't glue a bracket to the glass as the system was
running.

This is the float switch, screwed with the retaining nut to the brace.

This is how it will sit in the sump, in the return section.
This is the area where evaporation becomes apparent.

This is the cord where the float switch is spliced in.
You can see the one (white) wire that was not cut.

When my system is in place, I make sure the wiring is
water-resistant, so I wrapped it and point it upward so
water runs down the bag and down the wires. It is like a little umbrella
to avoid water getting into the wire nuts.

The bracket is in place in my sump. The white tubing
comes from my top off container and pours into the return section.

Side view. Currently the float is UP, and no water is
added. As evaporation occurs, the float will drop.

This container is designed to hold wrapping paper.
It cost less than $10 at Walmart, and fits in narrow spaces. It can
hold 10g of water. For my system, I can fill it up and it will top off
my 280g reef for two or three days. When I used the same system on my
29g, it would last 5 days.

I discovered that the water in your top off container
should not be taller than your sump. If it is, once the pump turns off,
gravity will continue to drain water until the water in the container
and the water in the sump match.

I hope that this information helps you understand how
it works and how it can be set up. It really isn't difficult or complicated,
and the suggestions I made will help you avoid some problem that may
occur. Try to plan well and you'll avoid accidents later.

Are there alternatives?
You can set up a system that is based on gravity with a float valve.
In this case, you'll need the container of water to be on a stand so
that it is higher than the sump. Instead of a float switch, use a float
valve. Install a drain (bulkhead) in your container and run tubing from
the container to the float valve. When the valve drops, water is allowed
to drain from the container into the sump. Once the water level rises
again, so does the float and the water is stopped until more is needed.

Other methods use dosing pumps, or inverting a bottle
or jug of water into the sump like a water cooler bottle. As it is needed,
some water pours out. Another method uses air to pressurize a sealed
container filled with water, forcing water out and into the tank via
thin tubing. Whatever method you choose, test and think it through so
it will be reliable and trouble-free!

12/08/05: I replaced
my top off container with something a little more sleek that hugs the
wall, and also allows more stored water volume. I needed two 1/2"
bulkheads, some PVC, and a new pump. See below.

These connections were glued permanently, as I didn't want to deal
with any leaks. Each container holds 10g, so I can have 20g of RO/DI
water available. The water level in the two containers is always the
same height, and lower gradually as top off is needed.

The Aqua
Lifter is a small pump that sucks water up from the bottom of the
container, and pumps it into the sump via the green tubing. It uses
3 watts of power, and can move up to 3g of water per hour. It runs silently,
like an air pump.

I made the end connection easy to remove, so that I can move it out
of my way when I need to access the power panel or return pump in the
rear corner of the fish room. This has worked out really well.

If you'd like to set up a system using a relay for additional safety, here is an excellent page with how-to pictures and explanations.